“Intake pipe pressure sensor” refers to a sensor which measures the pressure prevailing in the intake pipe. It does not necessarily have to be arranged directly in the intake pipe. In particular, it can also be a sensor usually referred to as a boost pressure sensor, which is arranged between the turbocharger compressor and the throttle valve ahead of the intake pipe, where the same pressure as in the intake pipe prevails when the throttle valve is open.
Modern internal combustion engines are often fitted with turbochargers to provide a higher engine power in comparison with naturally aspirated engines of the same swept volume. It is very common for vehicle manufacturers to offer engines of identical construction in different power versions. The individual engine components are in each case dimensioned for the most powerful version planned but can also be used in less powerful versions.
Owing to these available technical reserves of individual engine components, a number of commercial providers—tuners—have appeared, promising and—at least in some cases—achieving increases in power and/or fuel savings from the engines by modifications to the engine hardware and software. At the same time, however, there can be a negative impact on fuel emissions and/or on the life of the engine. From the point of view of manufacturers and legislators, therefore, these modifications are undesirable. It has also been observed that engines which have probably been damaged by tuning measures have been brought to repair garages after the reversal of the tuning measures with the expectation that they will be repaired at the expense of the manufacturer. For these reasons, there is a search for methods of reliably detecting such tuning measures in the engine controller.
For pressure-led turbocharged engines without an air mass meter, the cylinder air mass is calculated in the engine control device on the basis of the measured intake pipe pressure. On the basis of the calculated cylinder air mass, fuel is injected, and the engine produces torque. In factory condition, the engine controller correctly records the intake pipe pressure based on the measured value of the intake pipe pressure sensor, calculates the actual cylinder air mass and meters in sufficient fuel to ensure that the engine is operated at the desired fuel-air ratio. Minor deviations of the measured fuel-air ratio from its setpoint are compensated by the lambda controller implemented in the engine controller through correction of the fuel injection quantity.
If, starting from an engine operating point described in the engine controller, the actual intake pipe pressure is increased while the measured value of the intake pipe pressure remains unchanged—however this is achieved—this also leads to a real increase in the actual cylinder air mass, even if the cylinder air mass calculated in the engine control device does not rise. With a constant fuel quantity in the initial stage, this leads to dilution of the exhaust gas, i.e. to excess oxygen in the exhaust gas. The lambda probe measures this excess oxygen, and the engine control device increases the injected fuel mass in order to actually maintain the air-fuel ratio demanded. The engine thus actually has more air and more fuel available than demanded by the engine control device and actually produces more torque than demanded by the engine control device without the engine controller recording this. An increase of this kind in the actual intake pipe pressure is therefore one possible way of increasing the engine power.
A real increase of this kind in the intake pipe pressure relative to the measured value of the intake pipe pressure can be achieved, for example, if the measured intake pipe pressure is manipulated toward lower values by installing a tuning device between the intake pipe pressure sensor and the engine control device to manipulate the sensor signals accordingly.